Species Distribution mapping examples with R
Miles McBain
10 May, 2024
Introduction
This is Bank St Reserve. It’s a popular park in the inner north of Brisbane that is home to a small colony of Phascolarctos cinereus (Koala). There are large signs marking the space as Koala habitat near all public entrances, but unfortunately people walking dogs off leashes through the reserve is common. Attacks from dogs are a major source of Koala mortality in Greater Brisbane.
Banks St Reserve, Newmarket, Brisbane
Despite using Banks St as a weekly trail running track for the past six years, the authors of this paper have observed a Koala but once, when it was pointed out by a wildlife photographer. Recorded observations from the Atlas of Living Australia (ALA) for this area show why instance was potentially lucky. Koalas tend to favour the middle of the reserve, whereas the best running is to be had around the outside.
This author’s commonly used trail in pink, overlaid with hexbinned counts of recorded observations over the last 6 years
An examination of the timstamps of the ALA sightings recorded for this location showed they peaked in 2018 and have been in decline since. It is unclear whether this is due to a decline in population, or a decline in interest from citizen scientists. This question modtivated a study of the species spatial and temporal distribution for Greater Brisbane.
Recorded Koala observations in Banks St reserve are in decline over recent years.
Distribution of Phascolarctos cinereus across Greater Brisbane
Here we present an interactive map designed to display the distribution of Phascolarctos cinereus across Brisbane, and look at the question of declining observarions.
The map contains many layers which can be toggled on and off using the layer control in the top left corner. The layer initially selected displays counts of all recorded ocurrences binned using hexagonal spatial regions. This is useful for comparison at the suburb to city level, but detail is lost when zooming too far either in or out.
To observe different levels of distribtion detail the reader may try viewing:
- A point cloud layer of individual observation locations which has a ‘heat map’ like effect when zoomed out due to the application of additive colour blending. The points can be picked using the mouse cursor, which will display a tooltip containing some metadata relating to the observation.
- A dynamically computed heat map layer, which recomputes a 2-dimensional kernel density when the map is zoomed. It is useful for understanding relative frequency of occurence given the frame of refrence defined by the currently zoomed map window. It displays interesting detail at all levels of zoom.
To examine the question of the temporal distribution, a series of hexagonal binning layers were constructed each covering a 4-year span of the last 12 years. The colour scale of each layer remains relative to the highest observed hexagon count, aiding comparison. These can be toggled individually.